Image-forming apparatus

ABSTRACT

An image-forming apparatus equipped with an optical means, an electrostatic image-forming means and a control means. The optical means projects a scanned light beam to be controlled according to an image to be formed. The image-forming means receives the scanned light beam projected from the optical means and forms an image corresponding to the scanned light beam. The control means controls the optical means and the image-forming means.

FIELD OF THE INVENTION

This invention relates to an image-forming apparatus, and morespecifically, to an image-forming apparatus comprising an optical meansfor projecting a scanned light beam to be controlled according to animage to be formed, an electrostatic image-forming means for receivingthe scanned light beam projected from the optical means and forming animage corresponding to the scanned light beam, and a control means forcontrolling the optical means and the image-forming means.

DESCRIPTION OF THE INVENTION

In recent years, image-forming apparatuses of the above-described typehave been proposed and gained commercial acceptance as output devices orprinting devices in computer systems, word processing systems, etc. Theprior image-forming apparatuses, however, have problems or defects to beovercome. Among these are:

(1) In the image-forming means of the aforesaid image-forming apparatus,it is often necessary to get access to its various constituent elementsin order, for example, to supply or exchange developers for developmentof latent electrostatic images, or to clean or exchange anelectrostatographic material. It is important on the other hand that thevarious elements of the optical means should be held fully accurately atrequired positions and protected from contamination by the developers,dust and dirt, etc. Accordingly, it is important to its various elementsfrom being moved upon inadvertent touching by hand, or to avoid adhesionof developers, dust and dirt, etc. to the various elements owing tocareless handling. Since, however, the conventional image-formingapparatus accomodates the optical means, the image-forming means and thecontrol means together in a common housing, it is comparativelydifficult to get access to the various constituent elements of theimage-forming means without adversly affecting the optical means.

(2) In the optical means of the aforesaid image-forming apparatus, arotating polygon mirror assembly rotating at high speeds is generallyused as means for scanning a light beam. This rotating polygon mirrorassembly, however, produces considerable noises which are displeasing tothe operator and other persons.

(3) In the optical means of the aforesaid image-forming apparatus, alight beam generating means such as a layer tube is used. Such lightbeam generating means decreases in function after use for a long periodof time, and the light beam output is reduced. In order, therefore, toobtain the desired image, it is necessary to detect the light beam fromthe light beam generating means and when it is found that the output ofthe light beam is reduced, exchange the light beam generating means. Inthe conventional image-forming apparatus, a light beam detector isdisposed at the end portion of an exposure area of the image-formingmeans, i.e. an area to which the scanned light beam is projected fromthe optical means, which is not utilized for image formation, and thescanned light beam is detected by this light beam detector. Such adetecting method in the conventional image-forming apparatus, however,has some defects. For example, according to this method, the light beamfrom the light beam generating means is not directly detected. What isdetected is the scanned light beam scanned by the scanning means. Hence,a deterioration in the light beam caused by malfunctioning of deviceswhich affect the light beam, such as the scanning means and a modulatingmeans existing between the scanning means and the light beam generatingmeans, is detected as a deterioration in the light beam generatingmeans. Furthermore, the scanned light beam is projected onto the lightbeam detector repeatedly at time intervals. The duration of projection,however, is only very short, and the judgement of the scanned light beamso detected is relatively difficult.

(4) In the optical means of the aforesaid image-forming apparatus, it isimportant that its various constituent elements such as reflectingmirrors and lenses should be maintained clean and protected fromcontamination. In the conventional image-forming apparatus, however,contamination of the various constituent elements of the optical meanscannot be fully prevented, and the developers used in the image-formingmeans and dust and dirt adhere often to the various constituent elementsof the optical means.

(5) With the aforesaid image-forming apparatus, it is desired both toobtain an image of high quality, and to increase the speed of imageformation at the sacrifice of some reduction in image quality.Therefore, the speed of image formation is desired to be changed asrequired. The conventional image-forming apparatus cannot meet thisrequirement.

(6) The optical means of the aforesaid image-forming apparatus includesvarious elements such as light beam generating means, a condensing lens,a modulating means and reflecting mirrors. It is important that theseelements should be accurately held at the required positions. In theprior art, the positions of the various elements of the optical meansare adjusted by moving them on a trial-and-error basis. Such a method ofadjusting positions has the disadvantage that relatively long periods oftime are required and a sufficient accuracy in adjustment cannot beobtained.

SUMMARY OF THE INVENTION

It is a first object of this invention therefore to provide animage-forming apparatus in which one can easily get access to thevarious constituent elements of an image-forming means without adverselyaffecting an optical means.

A second object of this invention is to provide an image-formingapparatus in which noises generated by a rotating polygon mirrorassembly in an optical means are reduced.

A third object of this invention is to provide an image-formingapparatus in which a light beam from a light beam generating means of anoptical means can be directly detected without causing inconveniencesand the function of the light beam generating means can be checkedaccurately and easily.

A fourth object of this invention is to provide an image-formingapparatus in which the various constituent elements of an optical meansare fully prevented from being contaminated by developers used in animage-forming means or by dust and dirt in the environment.

A fifth object of this invention is to provide an image-formingapparatus in which the speed of image formation can be changed asrequired, and therefore it is possible to select whether to obtain animage of high quality or to obtain an image at a fairly high speed atthe sacrifice of some reduction in image quality.

A sixth object of this invention is to provide a method of opticaladjustment in an image-forming apparatus by which the positions of thevarious constituent elements of an optical means can be adjusted rapidlyand accurately.

In one aspect of this invention, the image-forming apparatus comprisesan image-forming means composed of an image-forming unit having a firsthousing, an optical means composed of an optical unit having a secondhousing and a control means composed of a control unit having a thirdhousing, in which the second housing is mounted on the first housing,and the third housing is mounted such that it can freely move between anoperating position at which it is located above the first housing andadjacent to the second housing and a non-operating position at which itis apart from the first housing.

In another aspect of this invention, the optical means has a rotatingpolygon mirror assembly which is substantially closed by a casing and anupstream side lens assembly and a downstream side lens assembly mountedon the casing.

In still another aspect, between a modulating means and a scanning meansof the optical means, there is provided a light beam detector whichshields a non-modulated light beam from the modulating means.

In yet another aspect, the optical means includes a housing havingformed therein an air sucking opening, an air discharge opening and alight beam passing opening through which a scanned light beam passes, aplurality of optical elements disposed within the housing, and an airblowing and cooling means for sucking air from outside the housingthrough the air sucking opening and discharging air out of the housingthrough the air discharge opening, in which the blowing and coolingmeans maintains at least the vicinity of the light beam passing openingof the housing under positive pressure and thus keeps the air inside thehousing flowing out through the light beam passing opening. Or the lightbeam passing opening of the housing is closed by a substantiallytransparent material.

In a further aspect of this invention, the optical means includes meansfor changing the diameter of a scanned light beam, and according to thechange of the diameter of the scanned light beam, the control meanschanges the feeding of image signals to the optical means and alsochanges the moving speed of an electrostatographic material in animage-forming means.

In an additional aspect of this invention, the positions of the variousconstituent elements of the optical means are adjusted by holdingadjusting jigs at predetermined positions.

The above and other objects of the invention will become apparent fromthe following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing one embodiment of the image-formingapparatus constructed in accordance with this invention;

FIG. 2 is a perspective view showing the image-forming apparatus of FIG.1 in a condition in which the cover is held at an open position;

FIG. 3 is a simplified sectional view of the image-forming apparatus ofFIG. 1;

FIG. 4 is a perspective view, partly broken away, of an optical means inthe image-forming apparatus of FIG. 1;

FIG. 5 is a perspective view showing the optical means of FIG. 4 partlydetached;

FIG. 6 is a top plan view of the optical means of FIG. 4 with the upperwall of its housing detached;

FIG. 7 is a simplified schematic view showing a second lens assembly inthe optical means of FIG. 4;

FIG. 8 is a perspective view, partly broken away, of a casing and itssurrounding structure in the optical means of FIG. 4;

FIG. 9 is a simplified schematic view of the path of a scanned lightbeam in the optical means of FIG. 4;

FIG. 10 is a top plan view showing a light shielding means and a lightbeam detecting means in the optical means of FIG. 4;

FIG. 11 is a perspective view showing the light shielding means andlight beam detecting means of FIG. 10;

FIG. 12 is a perspective view showing one embodiment of a firstadjusting jig used in optical adjustment in the optical means of FIG. 4;

FIG. 13 is a perspective view showing one embodiment of a secondadjusting jig used in optical adjustment in the optical means of FIG. 4;

FIG. 14 is a perspective view, partly broken away, of a modifiedembodiment of the casing and its surrouding structure in the opticalmeans;

FIG. 15 is a perspective view showing a modified embodiment relating toa light beam passing opening formed in the housing of the optical means;

FIG. 16 is a block diagram showing a control means in the image-formingapparatus of FIG. 1;

FIG. 17 is a simplified schematic view of one example of a characterproduced in the image-forming apparatus of FIG. 1; and

FIG. 18 is a simplified schematic view of one example of a characterproduced in the image-forming apparatus of FIG. 1 when the speed ofimage formation is doubled.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One specific embodiment of the image-forming apparatus constructed inaccordance with this invention will be described below in detail withreference to the accompanying drawings.

General Construction

With reference to FIGS. 1, 2 and 3, the general construction of theimage-forming apparatus shown generally at 2 is described.

The image-forming apparatus 2 shown includes an electrostaticimage-forming means shown generally at 4, an optical means showngenerally at 6 and a control means shown generally at 8. Theimage-forming means 4 is composed of an image-forming unit having afirst housing 10 which is relatively large and nearlyrectangular-parallelpipedal. The optical means 6 is composed of anoptical unit having a second housing 12 which is relatively small andnearly rectangular-parallelpipedal. The control means 8 is formed of acontrol unit having a third housing 14 which is relatively small andnearly rectangular-parallelpipedal. As will be described in detailhereinafter, the optical means 6 projects a scanned light beam to becontrolled according to an image to be formed. The image-forming means 4receives the scanned light beam projected from the optical means 6 andforms an image corresponding to the scanned light beam. The controlmeans 8 controls the optical means 6 and the image-forming means 4 asrequired.

The first housing 10 of the image-forming means 4 has legs 16 at itslower surface, and is placed on a suitable supporting base stand such asa floor surface. The second housing 12 of the optical means 6 is fixedto one side portion (the left side portion in FIG. 3) of a substantiallyhorizontal upper wall 18 of the first housing 10 by suitable means (notshown) such as screwing.

The image-forming apparatus 2 has a cover shown generally at 20. Thecover 20 has a nearly rectangular upper wall 22 and four side walls 24,26, 28 and 30 extending downwardly from the upper wall 22. As shown inFIGS. 2 and 3, a supporting plate 32, nearly rectangular in shape, isfixed to the inside surface of the upper wall 22 of the cover 20 bysuitable means (not shown) such as screwing. That end of the supportingplate 32 which is located on the left in FIG. 3 is pivotally linked toone side wall of the second housing 12, i.e. the upper end of theoutside surface of that side wall which is located on the left in FIG.3, by a pair of hinge linking means 34. Thus, the cover 20 is mountedsuch that it can be opened counterclockwise in FIG. 3 from its closedposition shown in FIGS. 1 and 3 about a hinge pin of the hinge linkingmeans 34 as a center. The supporting plate 32 has integrally formedtherein a downwardly extending portion 36 which extends downwardly fromits one side edge near its left end portion in FIG. 3. To the downwardlyextending portion 36 is pivotally linked by means of a pin 40 one end ofa gas spring means 38 known per se. The other end of the gas springmeans 38 extends to the inside of the first housing 10 through anopening 42 formed in the upper wall 18 of the first housing 10, and ispivotally linked by means of a pin 46 to a bracket 44 (FIG. 2) fixedwithin the first housing 10. The gas spring means 38 biases the cover 20counterclockwise in FIG. 3. There is also provided a locking mechanism48 (FIG. 3) for locking the cover 20 in the closed position against thebiasing action of the gas spring means 38. As illustrated in FIG. 3, thelocking mechanism 48 includes a locking member 52 mounted pivotally on apin 50 projecting rearwardly from the front side wall 24 of the cover20. A spring 54 is provided taut between the upper end portion of thelocking member 52 and the right side wall 26 of the cover 20. The spring54 biases the locking member 52 clockwise in FIG. 3 and elasticallyholds it at a locking position shown in FIG. 3. A pressing member 56 isfixed to the locking member 52, and the free end of the pressing member56 is located within an opening 58 formed in the right side wall 26 ofthe cover 20. On the other hand, an opening 60 is formed at that portionof the upper wall 18 of the first housing 10 which corresponds to thelocking member 52, and an engaging pin 62 is disposed below the opening60. When the cover 20 is pivoted clockwise in FIG. 3 from its openposition shown in FIG. 2 and brought to a point near its closed positionshown in FIG. 3, the hook-like lower end portion of the locking member52 advances into the first housing 10 through the opening 60 and itsundersurface abuts against the engaging pin 62. Hence, when pivoting ofthe cover 20 is continued, the action of the engaging pin 62 causes thelocking member 52 to pivot counterclockwise in FIG. 3 against theelastic biasing action of the spring 54. When the cover 20 is pivoted tothe closed position shown in FIG. 3, the hook-like lower end portion ofthe locking member 52 goes beyond the engaging pin 62. As a result, thelocking member 52 is pivoted clockwise and returned to the lockingposition by the elastic biasing action of the spring 54. Thus, as shownin FIG. 3, the hook-like lower end portion of the locking member 52comes into engagement with the engaging pin 62 whereby the cover 20 islocked in the closed position shown in FIG. 3. To open the cover 20, thehook-like lower end portion of the locking member 52 is detached fromthe engaging pin 62 by pushing with a finger the free end of thepressing member 56 fixed to the locking member 52 and thereby pivotingthe locking member 52 counterclockwise. Consequently, the cover 20 ispivoted counterclockwise in FIG. 3 by the biasing action of the gasspring means 38. When the cover 20 has been pivoted to its open positionshown in FIG. 2, the biasing action of the gas spring means 38 comesinto equilibrium with the moment ascribable to the weight of the cover20 (as will be clear from the following description, the weight alsoincludes the weight of the control means 8 mounted on the cover 20). Thecover 20 is thus maintained stably at the open position shown in FIG. 2.

In the illustrated image-forming apparatus 2, the housing of the conrolmeans 8, namely the third housing 14, is mounted in the cover 20 byfixing its upper surface to the supporting plate by suitable means (notshown) such as a setscrew. Since the control means 8 is relatively lightin weight, mounting of the third housing 14 in the cover 20 does notcause any inconvenience. As is clearly seen from FIG. 3, when the cover20 is at its closed position at which it covers the upper surface of thefirst housing 10 of the image-forming means 4 and the second housing 12of the optical means 6, the third housing 14 mounted in the cover 20 andmoving together with the cover 20 is at its operating position at whichit is located adjacent to the second housing 12 and above the firsthousing 10 with some distance from the upper wall 18 of the firsthousing 10. On the other hand, when the cover 20 is at its open positionat which it exposes the upper surface of the first housing 10 and thesecond housing 12 to view, the third housing 14 is brought to itsnon-operating position at which it is apart from the upper surface ofthe first housing 10, as is clear from FIG. 2.

As shown in FIGS. 2 and 3, a relatively large opening 64 which enablesaccess to the inside of the first housing 10 is formed in at least apart of that area of the upper wall 18 of the first housing 10 which isexposed to view when the cover 20 is held at the open position to holdthe third housing 14 at the non-operating position. The opening 64 isclosed by a freely openable and closable closure member 68 whose one endedge (the left end edge in FIG. 3) is pivotally connected to the upperwall 18 by a pair of hinge linking means 66.

As will be clear from the description made hereinafter, it isocassionally necessary to get access to the various constituent elementsaccommodated in the first housing 10 in order, for example, to supply orexchange developers or to clean or exchange the electrostatographicmaterial. In this case, the cover 20 is first pivoted to the openposition to bring the third housing 14 to its non-operating position.Then, the closure member 68 is pivoted counterclockwise in FIG. 3 fromits closed position shown in FIG. 3 to expose the opening 64. As aresult, one can easily get access to the inside of the first housing 10through the opening 64. As will also be clear from the description madehereinafter, the second housing 12 accommodates therein variousconstituent elements which must be held fully accurately at the requiredpositions and protected from contamination by the developers, dust anddirt, etc. When access to the inside of the first housing 10 is obtainedas described above, the second housing 12 remains unmoved and unopened,and therefore, there is no fear of adverse effects on the variousconstituent elements disposed in the second housing 12.

Electrostatic Image-Forming Means

Now, the electrostatic image-forming means 4 composed of theimage-forming unit having the first housing 10 will be described indetail.

With reference to FIG. 3, a cylindrical rotating drum 70 is rotatablymounted nearly centrally in the first housing 10. A suitableelectrostatographic material 72 is disposed on the peripheral surface ofthe rotating drum 70.

Around the rotating drum 70 to be rotated in the direction of an arrow74 are disposed a charging corona discharge device 76, a developingmeans generally shown at 78, a transfer corona discharge device 80, apeeling corona discharge device 82 and a cleaning means shown generallyat 84 in this order in the rotating direction of the drum 70. Thecharging corona discharge device 76 substantially uniformly charges theelectrostatographic material 72 to a specified polarity. An exposurearea 86 exists between the charging corona discharge device 76 and thedeveloping means 78. In the exposure zone 86, a scanned light beamadvancing from the optical means 6 to the inside of the first housing 10through an opening 90 formed in the upper wall 18 of the first housing10 is projected onto the electrostatographic material 72, thereby toform a latent electrostatic image corresponding to the scanned lightbeam on the electrostatographic material 72. The opening 90 is of anelongated shape extending axially of the rotating drum 70, namely in adirection perpendicular to the sheet surface in FIG. 3. The innersurface of the upper wall 18 which is near the opening 90 and thesurface of frame materials of the charging corona discharge device 76and the developing means 78 which face the path of the scanned lightbeam shown by an arrow 88 are conveniently coated in a dark color orcovered with a felt or the like of a dark color in order to re-reflectthe scanned light beam reflected from the electrostatographic material72 without absorption. This prevents the scanned light beam reflected bythe electrostatographic material 72 from being reflected again towardthe electrostatographic material 72 and thus disturbing the latentelectrostatic image formed on it.

The illustrated developing means 78 includes a main developing portion92 having a casing 94 holding a two-component developer 96 composed ofcarrier particles and toner and a developer applicator means 98 disposedwithin the casing 94, and a toner supplying portion 100 for supplyingtoner 102 therein to the casing 94 as required. The developer applicatormeans 98 of the main developing portion 92 is rotated in the directionof an arrow 104 and magnetically attracts a developer 96 in the casing94 to its surface to form a so-called "magnetic brush", and applies themagnetic brush to the electrostatographic material 72 through an opening106 formed in the casing 94. Thus, the toner is applied to the latentelectrostatic image formed on the electrostatographic material 72 todevelop it to a toner image. The transfer corona discharge device 80applies a corona discharge to the back surface of a copying paper to becontacted with the surface of the electrostatographic material 72 in atransfer zone 108 to transfer the toner image on the electrostatographicmaterial 72 to the copying paper. The peeling corona discharge device 82applies corona discharge to the back surface of the copying paperimmediately downstream of the transfer zone 108 to peel theelectrostatically adhering copying paper from the surface of theelectrostatographic material 72.

The cleaning means 84 has a blade 110 made of an elastic material to bepressed against the surface of the electrostatographic material 72, andby the action of the blade 110, removes residual toner particles fromthe electrostatographic material 72.

The image-forming means 4 further includes a copying paper feed meansshown generally at 112, and a copying paper conveying means showngenerally at 114 for conveying a copying paper fed from the copyingpaper feed means 112 through the transfer zone 108. The paper feed means112 has a cassette receiving stand 116, a copying paper cassette 118mounted detachably on the cassette receiving stand 116 through anopening 110 formed on the right side wall 117 of the first housing 10,and a feed roller 120. The feed roller 120 is rotated selectively in thedirection shown by an arrow and delivers a plurality of copying papersheets stacked in the copying paper cassette 118 one by one. The copyingpaper conveying means 114 includes a pair of conveying rollers forconveying a copying paper fed from the paper feed means 112, guide platemeans 124, 126 and 128 for guiding the copying paper conveyed by thepair of conveying rollers to the transfer zone 108, a sucking-typeconveying and guiding mechanism 130 for conveying and guiding thecopying paper peeled from the electrostatographic material 72, a pair offixing rollers 132, guide plate means 134 and 136, a pair of deliveryrollers 138, and a receiving tray 144 for receiving the copying paperdischarged from the pair of delivery rollers 138 through an opening 142formed in the left side wall 140 of the first housing 10. One of thepair of fixing rollers 132, i.e. the roller 132 located above, hasformed therein a heating element. The pair of fixing rollers 132 pressand heat the surface of the copying paper having a toner imagetransferred thereto from the electrostatographic material 72, andthereby fix the toner image onto the copying paper.

The aforesaid construction itself of the image-forming means 4 isconventional and does not constitute any novel feature of theimage-forming apparatus 2 constructed in accordance with this invention.Accordingly, a detailed description of the aforesaid construction in theimage-forming means 4 will be omitted in the present specification.

When in the image-forming means 4 described above, the toner in thetoner supplying portion 100 of the developing means 78 has been consumedand it is necessary to load the toner in the toner supplying portion100, the cover 20 is pivoted to the open position shown in FIG. 2 tobring the third housing 14 (i.e., the housing of the control means 8) atthe non-operating position shown in FIG. 2, and then the closure member68 is opened to expose the opening 64 formed in the upper wall 18 of thefirst housing 10. As a result, the toner can be loaded into the tonersupplying portion 100 through the opening 64. In the case of repair ofthe developing means 78 or the cleaning or exchanging of theelectrostatographic material 72, the developing means 78 and therotating drum 70 can be detached and taken out as required through theopening 64.

Optical Means

The optical means 6 composed of the optical unit having the secondhousing 12 will now be described in detail.

(A) Construction of the Optical Means

With reference to FIG. 4, the housing of the optical means 6, i.e. thesecond housing 12, is defined by a bottom wall 146, four side walls 148,150, 152 and 154 and an upper wall 156. With reference to FIGS. 5 and 6as well as FIG. 4, a light beam generating means 158, a first reflectingmirror assembly 160, a first lens assembly 162, a second reflectingmirror assembly 164, a modulating means 166, a second lens assembly 168(FIGS. 5 and 6), a scanning means 170 (FIG. 6), a third lens assembly172, a third reflecting mirror assembly 174, a fourth reflecting mirrorassembly 176 and a fifth reflecting mirror assembly 178 are mounted onthe bottom wall 146 of the second housing 12.

The light beam generating means 158 is constructed of a gas laser tubehaving a cylindrical casing 180. The light beam generating means 158 ismounted on the bottom wall 148 by a pair of supporting means 182 suchthat it is adjacent to the side wall 148 and extends substantiallyparallel to the bottom wall 146 and the side wall 148. Each of the pairof supporting means 182 constists of a supporting stand 184 fixed to thebottom wall 146 and a nearly semicircular arcuate holding member 186cooperating with the supporting stand 184. A nearly semicircular recessis formed on the upper surface of the supporting stand 184. The lightbeam generating means 158 is positioned in the recess of the supportstand 184 and then the holding member 186 is provided astride the lightbeam generating means 158. Then, the flange portions at both ends of theholding member 186 are fixed to the supporting stand 184 by a setscrew188, thereby mounting the light beam generating means 158 on the bottomwall 146.

The first reflecting mirror assembly 160 is comprised of a supportingstand 190 fixed to the bottom plate 146, a nearly U-shaped holdingmember 192 mounted on the support stand 190, a supporting member 194mounted on the holding member 192, and a mirror 196 secured to thesupporting member 194. The holding member 192 is mounted on thesupporting stand 190 so that its rotating angular position about asubstantially perpendicular axis can be freely adjusted. The supportingmember 194 is mounted on the holding member 192 so that its rotatingangular position about a substantially horizontal axis can be freelyadjusted.

The first lens assembly 162 is comprised of a supporting member 198fixed to the bottom wall 146 so that its position can be freelyadjusted, and a condensing lens 200 fixed within a through hole formedin the upper portion of the supporting member 198.

The second reflecting mirror assembly 164 is substantially the same asthe first reflecting mirror assembly 160 described above, and iscomprised of a supporting stand 202 fixed to the bottom wall 146, anearly U-shaped holding member 204 mounted on the supporting stand 202,a supporting member 206 mounted on the holding member 204 and a mirror208 fixed to the supporting member 206. The holding member 204 ismounted on the supporting stand 202 such that its rotating angularposition about a substantially perpendicular axis can be freelyadjusted, and the supporting member 206 is mounted on the holding member204 such that its rotating angular position about a substantiallyhorizontal axis can be freely adjusted.

The modulating means 166 may be constructed of a suitable modulator suchas a known acousto-optical modulator, and is fixed to a supporting stand210 which is fixed to the bottom plate 146 in such a manner that itsposition can be freely adjusted.

The second lens assembly 168 has a cylindrical lens frame 212. Asschematically shown in FIG. 7, one collimator lens 214 and a pluralityof (two in the drawing) expander lenses 216 are disposed within the lensframe 212. The lens frame 212 is mounted on the bottom wall 146 by aconventional supporting means 218 composed of a pair of supportingmembers so that its longitudinal position can be freely adjusted. Oneend portion of the lens frame 212 extends through the side wall of acasing shown generally at 220 and described in detail hereinafter, andis mounted on the casing 220 such that it can move freely in thelongitudinal direction.

With reference to FIG. 8 also, the scanning means 170 is constructed ofa rotating polygon mirror assembly known per se which has a nearlycylindrical case 222. The case 222 of the rotating polygon mirrorassembly has accommodated therein a plurality of (8 in the drawing)scanning mirrors 224 (FIGS. 6 and 9) arranged in a polygonal shape andan electric motor (not shown) for rotating the scanning mirrors 224 athigh speeds. An opening 226 is formed in the case 222 so as to permitfalling of a light beam upon the scanning mirrors 224 and outgoing of ascanned light beam from the scanning mirrors 204. An annular holdingmember 230 is fixed around the case 222. The annular holding member 230is fixed to a supporting stand 232 secured to bottom wall 146. Thus, thescanning means 170 composed of the rotating polygon mirror assembly isfixed to a predetermined position on the bottom wall 146.

With reference to FIGS. 5, 6 and 8, the scanning means 170 is surroundedby the casing 220. The casing 220 has a nearly arcuate upstanding sidewall 234 extending along the contour of the supporting stand 232, anupstanding front wall 236 fixed between the two ends of the side plate234 and an upper wall 238 closing the upper surface of the casing 220.The lower surface of the casing 220 is closed by the supporting stand232 and the bottom wall 146. The side wall 234 of the casing 220 hasformed therein a circular opening for incoming of a light beam throughwhich one end portion of the lens frame 212 of the second lens assembly168 extends. Preferably, an annular sealing material 242 made of aflexible material such as rubber is disposed in the opening 240 so as toseal substantially the space between the side wall 234 and the lensframe 212 while permitting movement of the lens frame 212 in thelongitudinal direction. A nearly circular opening for outgoing of alight beam is formed in the front wall 236 of the casing 220. Thisopening, in cooperation with an arcuate recessed portion 244 (FIG. 8)formed in the front end of the supporting stand 232, defines a mountingportion for the third lens assembly 172. The third lens assembly 172 hasa short bylindrical lens frame 246, a so-called f-θ lens 248 fixedwithin the lens frame 246, and a linking plate 250 fixed to theperipheral surface of the lens frame 246. The third lens assembly 172 ismounted at a predetermined position by inserting one end portion of thelens frame 246 in a circular mounting portion defined by the openingformed in the front wall 236 and the arcuate recessed portion 244 formedin the supporting stand 232, and fixing the linking plate 250 to thefront wall 236.

It will be understood from the above description of the casing 220 thatthe scanning means 170 constructed of the rotating polygon mirrorassembly is substantially closed by the casing 220 and the two lensassemblies mounted on the casing 220, i.e. the second lens assembly 168located upstream of the scanning means 170 as viewed in the advancingdirection of the light beam and the third lens assembly 172 locateddownstream of the scanning means 170 as viewed in the advancingdirection of the light beam. As is well known, in the rotating polygonmirror assembly, the scanning mirrors 224 are rotated at high speeds,and therefore considerably noises are produced. Propagation of thesenoises can be considerably reduced by substantially closing the rotatingpolygon mirror assembly as described above.

With reference to FIGS. 4 and 6, a pair of supporting stands 252 spacedfrom each other a predetermined distance are fixed to the bottom wall146. The third reflecting mirror assembly 174 and the fifth reflectingmirror assembly 174 are mounted between the pair of supporting stands252. The third reflecting mirror assembly 174 has a supporting plate 254both ends of which are fixed respectevely to the side edges of thesupporting stand 252. A mirror 258 is fixed to the back surface of thesupporting plate 254 by means of a pair of fixing devices 256. Thesupporting plate 254 has formed therein an elongated opening extendingin its longitudinal direction, and the main front surface portion of themirror 258 is exposed to view through this opening. The fifth reflectingmirror assembly 178 has a supporting plate 262 having short shafts 260formed at its opposite ends. By rotatably mounting the short shafts 260formed at the opposite ends of the supporting plate 262 in holes formedat the upper end portions of the supporting stand 252 and hampering therotation of the short shafts 260 by a setscrew 264 which advances intoeach of the holes from the side edge of each of the supporting stands252 and abuts against each short shaft 260, the supporting plate 262 ismounted between the pair of supporting stand 252 such that its rotatingangular position about its longitudianl axis can be freely adjusted. Amirror 268 is fixed to the back surface of the supporting plate 262 by apair of fixing devices 266. The supporting plate 262 has formed thereinan elongated opening which extends longitudinally thereof, and the mainfront surface portion of the mirror 268 is exposed to view through thisopening.

With reference to FIGS. 5, 6 and 9, an elongated recessed portion 270having a nearly triangular cross section is formed in the bottom wall146, and the fourth reflecting mirror assembly 176 has a mirror 272fixed to the recessed portion 270 by a pair of fixing devices 273.

In the optical means 6 described above, as shown by the one-dot chainlines in FIGS. 4, 5 and 6, a laser light beam generated by the lightbeam generating means 158 arrives at the mirror 196 of the firstreflecting mirror assembly 160 and is reflected by the mirror 196. Thereflected light beam passes through the condenser lens 200 of the firstlens assembly 162, and arrives at the mirror 208 of the secondreflecting mirror assembly 164 where it is reflected by the mirror 208.The reflected mirror then falls upon the modulating means 166. As willbe described hereinafter, the modulating means 166 modulates the laserlight beam according to image signals fed from the control means 8 (FIG.3). As will be clear from the description made hereinafter, only amodulated primary light beam among the laser light beams coming from themodulating means 166 falls upon the second lens assembly 168. The laserlight beam incident to the second lens assembly 168 is converyed to aparallel light by being passed through the collimator lens 214 (FIG. 7),and then by passing it through a plurality of expander lenses 216 (FIG.7), its beam diameter is adjusted to the desired value. The laser lightbeam which has passed through the second lens assembly 168 arrives atthe scanning mirrors 224 of the scanning means 170, and by the action ofthe scanning mirrors 224 rotating at high speeds, it is projected as ascanned laser light beam reciprocally scanned in the left-rightdirections in FIG. 6. The scanned laser light beam projected from thescanning means 170 passes through the f-θ lens 248 of the third lensassembly 172, and thereafter is reflected successively by the mirror 258of the third reflecting mirror assembly 174, the mirror 274 of thefourth reflecting mirror assembly 176 and the mirror 268 of the fifthreflecting mirror assembly 178. The laser light beam reflected by thefifth reflecting mirror assembly 178 goes out from the second housing 12after it has passed through the light beam passing opening 276 formed inthe bottom wall 146, advances into the first housing 10 through theopening 90 formed in the upper wall 18 of the first housing 10, andarrives at the electrostatographic material 72 disposed on theperipheral surface of the rotating drum 70 in the exposure zone 86 asstated hereinabove. It is necessary that the mirrors 258, 274 and 268 ofthe third to fifth reflecting mirror assemblies 174, 176 and 178 aredisposed substantially parallel to the central axis of the rotating drum70 (FIG. 3), and the opening 276 formed in the bottom wall 146 should bein alignment with the opening 90 formed in the upper wall 18 of thefirst housing 10 and extends substantially parallel to the central axisof the rotating drum 70. On the other hand, it is preferred that theangle of the mirror 268 of the fifth reflecting mirror assembly 178 isprescribed so that the path of the laser light beam ranging from themirror 268 of the fifth reflecting mirror assembly 178 to theelectrostatographic material 72 slightly deviates with respect to thecentral axis of the rotating drum 70. If the path of the laser lightbeam ranging from the mirror 268 to the electrostatographic material 72is in alignment with the central axis of the rotating drum 70, a part ofthe laser light beam arriving at the electrostatographic material 72 isreflected by the electrostatographic material 72 and then by beingreflected by the mirrors 268, 274 and 258, returns to the scanningmirrors 224 of the scanning means 170, and thereafter is again projectedonto the electrostatographic material 72. This may possibly result indisturbance of the latent electrostatic image formed on theelectrostatographic material 72.

In the illustrated optical means 6, a shielding means is provided whichcauses only a modulated primary light beam among the laser light beamsfrom the modulating means 166 to fall upon the second lens assembly 168.With reference to FIGS. 10 and 11 together with FIGS. 5 and 6, anannular flange 278 is formed integrally at the upstream end, viewed inthe advancing direction of the light beam, of the cylindrical lens frame212 of the second lens assembly 168, and a light shielding means 280 isfixed to the flange 278. The light shielding means 280 is comprised of apair of light shielding plates 282 and 284 spaced from each other somedistance and fixed to the flange 278. As can be seen from FIG. 10, thedistance between the pair of light shielding plates 282 and 284 issubstantially equal to the diameter of a modulated primary light beam M1existing when image signals, i.e. modulation signals, have been fed tothe modulating means 166, and the light shielding plates are positionedso that they permit passage of only the modulated primary light beam M1from the modulating means 166. A non-modulated light beam NM existingwhen no image signal is fed to the modulating means 166 is shut off bythe light shielding plate 282 and cannot fall upon the second lensassembly 168. As is well known to those skilled in the art, when imagesignals have been fed to the modulating means 166, not only themodulated primary light beam M, by also weak secondary, tertiary . . .light beams having a larger angle of deflection to the non-modulatedlight beam NM than the angle of deflection of the modulated primarylight beam M1 exist. These secondary, tertiary, . . . light beams areshut off by the light shielding plate 284 and cannot fall upon thesecond lens assembly 168.

A light beam detector 286 which may be constructed of a photocell, forexample, is disposed in that area of the light shielding plate 282 uponwhich a non-modulated light beam NM falls. The light beam detector 286produces a signal corresponding to the intensity of the projectednon-modulated light beam NM and feeds it to the control means 8 to bedescribed in detail hereinafter. The control means 8 compares the signalfed from the light beam detector 286 with a predetermined standardvalue, and produces a warning signal when the intensity of thenon-modulated light beam NM falls below a predetermined value as aresult of the degradation of the light beam generating means 158. Whenthe warning signal is produced, a warning lamp (not shown) provided in apanel 288 (FIG. 1) disposed on the surface of the cover 20 is turned on.

Since the light beam detector 286 detects the non-modulated light beamNM not used for the formation of a latent electrostatic image in theimage-forming means 4, it does not adversly affect the image-formingaction of the means 4. Furthermore, because the non-modulated light beamNM can exist for a relatively long period of time, a signal which thelight beam detector 286 produces according to the intensity of thenon-modulated light beam NM also exists over a relatively long period oftime, and comparison, etc. of the signal can be easily and accuratelyeffected. Furthermore, since the light beam detector 286 detects thenon-modulated light beam NM, it can directly examine a light beamgenerated by the light beam generating means without being affected bythe function of the modulating means 166.

(B) Optical Adjustment in the Optical Means

It will be easily understood that in the above optical means 6, it isimportant for the optical axis of the modulated primary light beam M1from the modulating means to be fully and precisely in alignment withthe optical axis of the second lens assembly 168. For this purpose, itis important that the light beam generating means 158, the mirror 196 ofthe first reflecting mirror assembly 160, the condensing lens 200 of thefirst lens assembly and the modulating means 166 should be held fullyprecisely at predetermined positions. In order to enable such apositioning operation to be carried out rapidly and easily, one specificembodiment of this invention utilizes one first adjusting jig 290 of theshape shown in FIG. 12 and two second adjusting jigs 292 of the shapeshown in FIG. 13. The first adjusting jig 290 shown in FIG. 12 has ahorizontal base portion 294 and an upstanding portion 296 extendingupwardly from the upper surface of the base portion 294. A positioningprojection 298 is formed on the lower surface of the base portion 294.On the other hand, a horizontally extending elongated beam hole 300 isformed in the upstanding portion 296 at a predetermined height H fromthe lower surface of the base portion 294. The size of the beam hole 300in the height direction may be about 0.8 mm. Preferably, the firstadjusting jig 290 is formed symmetrical with respect both to a centralvertical surface parallel to the upstanding portion 296 and a centralvertical surface perpendicular to the upstanding portion 296 in orderthat it can be used without considering its surface and back (thesurface and back of the upstanding portion 296). Each of the secondadjusting jigs 292 shown in FIG. 13 also has a horizontal base portion302 and an upstanding portion 304 extending upwardly from the uppersurface of the base portion 302. A positioning projection 306 is formedon the lower surface of the base portion 302. On the other hand, threebeam holes, i.e. a central beam hole 308 located centrally, and two sidebeam holes 310 located on both sides of the central beam hole 308 eachat an equal distance from the central beam hole 308 are formed in theupstanding portion 304 at a predetermined height H (which issubstantially equal to the height H in the first adjusting jig 290). Thediameters of the beam holes 308 and 310 may be about 0.8 mm. Preferably,the second adjusting jigs 292 are also formed symmetrical both withrespect to a central vertical surface parallel to the upstanding portion304 and a central vertical surface perpendicular to the upstandingportion 304 in order that they can be used without consideration totheir surface and back. As will be seen from the description madehereinafter, only one side beam hole 310 may be sufficient, but twoholes 310 are formed in this embodiment so that the jigs can be usedwithout consideration to their surface and back.

With reference to FIGS. 5 and 6, a plurality of positioning recesseshaving shapes corresponding to the shapes of the projections 298 and 306are formed on the upper surface of the bottom wall 146 so as to positionthe first and second adjusting jigs 290 and 292 therein. Specifically, afirst recess 312 is formed at a predetermined position between the lightbeam generating means 158 and the first reflecting mirror assembly 160.A second recess 314 is formed at a predetermined position between thefirst reflecting mirror assembly 160 and the first lens assembly 162. Athird recess 316 is formed between the first lens assembly 162 and thesecond reflecting mirror assembly 164. A fourth recess 318 is formedbetween the modulating means 166 and the second lens assembly 168.

A method of optical adjustment utilizing the first and second adjustingjigs 290 and 292 will now be described.

In the first step of adjustment, a light beam from the light beamgenerating means 158 is adjusted to a predetermined height H from theupper surface of the bottom wall 146. As is well known to those skilledin the art, in a gas laser tube constituting the light beam generatingmeans 158, the central axis of the cylindrical casing 180 does notnecessarily align with the optical axis of the generated light beam, andfrequently some error exists between them. Hence, even when the casing180 is positioned fully accurately by the pair of supporting means 182so that it extends parallel to the bottom wall 146 at the predeterminedheight H from the upper surface of the bottom wall 146, the optical axisof the generated light beam frequently does not have the predeterminedheight H. To adjust the optical axis of the generated light beam to thepredetermined height H, the first adjusting jig 290 is held at apredetermined position between the light beam generating means 158 andthe first reflecting mirror assembly 160 by inserting the projection 298of the first adjusting jig 290 into the first recess 312. Then, byrotating the casing 180 with its central axis as a center so that thegenerated light beam passes through the beam hole 300 of the firstadjusting jig 290, as shown by the two-dot chain line in FIG. 5. Thus,the light beam from the light beam generating means 158 is adjusted suchthat it advances substantially parallel to the bottom wall 146 at thepredetermined height H. After this adjustment is over, the firstadjusting jig 290 is removed.

In the second step of adjustment, the position of the mirror 196 of thefirst reflecting mirror assembly 160 is adjusted. In performing thisadjustment, one second adjusting jig 292 is held at a predeterminedposition between the first reflecting mirror assembly 160 and the firstlens assembly 162 by inserting the projection 306 of the secondadjusting jig 292 into the second recess 314, and the other secondadjusting jig 292 is held at a predetermined position between the firstlens assembly 162 and the second reflecting mirror assembly 164 byinserting the projection 306 of the other second adjusting jig 292 intothe third recess 316, as shown by the two-dot chain line in FIG. 5.Then, the first lens assembly 162 is detached, and the position of themirror 196 of the first reflecting mirror assembly 160 is adjusted sothat the light beam reflected by the mirror 196 passes through one ofthe two side beam holes 310 of the second adjusting jig 292, i.e. theside beam hole 310 located on the left in the advancing direction of thelight beam. The position of the mirror 196 is adjusted by adjusting therotating angular position of the retaining member 192 about asubstantially vertical axis and the rotating angular position of thesupporting member 194 about a substantially horizontal axis. When theadjustment is over, the second adjusting jig 292 positioned between thefirst reflecting mirror assembly 160 and the first lens assembly 162 isremoved. However, the second adjusting jig 292 positioned between thefirst lens assembly 162 and the second reflecting mirror assembly 164 isretained without removal.

In the third step of adjustment, the first lens assembly 162 detached inthe second step is installed. The installing position of the first lensassembly 162 is adjusted so that the light beam passing through thecondensing lens 200 passes through the central beam hole 308 of thesecond adjusting jig 292 positioned between the second lens assembly 162and the second reflecting mirror assembly 164. When this adjustment iscompleted, the second adjusting jig 292 is removed.

In the fourth step of adjustment, the position of the mirror 208 of thesecond reflecting mirror assembly 164 is adjusted. In performing thisadjustment, the second adjusting jig 292 is held at a predeterminedposition between the modulating means 166 and the second lens assembly168 by inserting the projection 306 of the second adjusting jig 292 intothe fourth recess 318 as shown by the two-dot chain line in FIG. 5. Themodulating means 166 and the supporting stand 210 to which themodulating means 166 is fixed are detached. Then, the position of themirror 208 of the second reflecting mirror assembly 164 is adjusted sothat the light reflected by the mirror 208 passes through the centralbeam hole 308 of the adjusting jig 292. The position of the mirror 208is adjusted by adjusting the rotating angular position of the holdingmember 204 about a substantially vertical axis and the rotating angularposition of the supporting member 206 about a substantially horizontalaxis.

In the fifth step of adjustment, the supporting stand 210 and themodulating means 166 detached in the fourth step are installed. Theinstalling position of the supporting stand 210 is adjusted so that thenon-modulated light beam NM (see FIG. 10) from the modulating means 166passes through one of the two side beam holes 310 of the secondadjusting jig 292 positioned between the modulating means 166 and thesecond lens assembly 168, i.e. the side beam hole 310 located on theleft in the advancing direction of the light beam, and the modulatedprimary light beam M1 (see FIG. 10) from the modulating means 166 passesthrough the central beam hole 308 of the second adjusting jig 292. Afterthe adjustment is completed, the second adjusting jig 292 is removed.

By the procedure described above, the optical axis of the modulatedprimary light beam M1 (see FIG. 10) from the modulating means 166 isbrought into fully precise alignment with the optical axis of the secondlens assembly 168.

In the aforesaid embodiment, the second adjusting jig 292 having thecentral beam hole 308 and the side beam holes 310 (i.e., the secondadjusting jig 292 used at the time of adjusting the position of themodulating means 166) is also used in adjusting the positions of themirror 196 of the first reflecting mirror assembly 160, the condensinglens 200 of the first lens assembly 162, and the mirror 208 of thesecond reflecting mirror assembly 164. In adjusting the positions ofthese members, the side beam holes 310 are not necessary. Accordingly,separately prepared adjusting jigs having only a central beam hole maybe used in adjusting the positions of these members.

(c) Correction of Production Errors of Lenses in the Optical Means

In the optical means 6 described above, it is important that the beamdiameter of the scanned light beam projected should be prescribed at apredetermined value. The diameter of the scanned light beam depends uponthe characteristics and positions of the condensing lens 200, thecollimator lens 214 and expander lenses 216 (FIG. 7). Even when theselenses 200, 214 and 216 are precisely held at predetermined positions,the beam diameter of the scanned light beam may often deviate from apredetermined value owing to errors of the lenses 200, 214 and 216 incharacteristics caused by production errors.

In the illustrated embodiment constructed in accordance with the presentinvention, the lens frame 212 of the second lens assembly 168 having thecollimator lens 214 and expander lenses 216 (FIG. 7) is mounted so thatits position in the longitudinal direction can be freely adjusted. Byadjusting the lengthwise position of the lens frame 212 (i.e., thepositions of the collimator lens 214 and the expander lenses 216), thediameter of the scanned light beam can be corrected to the predeterminedvalue. In order to perform the position adjustment of the lens frame 212easily, it is possible, for example as shown in FIG. 14, to form aninternal thread on the inner circumferential surface of the light beamincoming opening 240 formed on the side wall 234 of the casing 220 andan external thread 320 cooperating with the internal thread at one endportion of the lens frame 212, and to adjust the longitudinal positionof the lens frame 212 by rotating the lens frame 212 about its centralaxis as acenter and thus varying the degree of screwing between theinternal thread and the external thread 320.

If desired, instead of, or in addition to, the adjustment of thediameter of the scanned light beam by adjusting the longitudinalposition of the lens frame 212, the diameter of the scanned light beammay be adjusted by mounting the collimator lens 214 (FIG. 7) within thelens frame 212 by a suitable means so that its postion can be freelyadjusted and adjusting the position of the collimator lens 214 in thelongitudinal direction of the lens frame 212. Alternatively, thediameter of the scanned light beam can be adjusted by constructing theexpander lenses 216 (FIG. 7) from zoom lenses known in the field ofcameras and operating the zoom lenses.

(D) Air Blowing in the Optical Means

With reference to FIGS. 4, 5 and 6, the housing of the optical means 6,i.e. the second housing 12, is divided into a first space 326 and asecond space 328 by a first partitioning wall 322, the casing 220 and asecond partitioning wall 324. The first partitioning wall 322 extendsbetween the side wall 150 of the second housing 12 and the casing 220,and the second partitioning wall 324 extends between the casing 220 andthe side wall 152. A plurality of vent openings 330 are formed in thefirst partitioning wall 322. The light beam generating means 158, thefirst reflecting mirror assembly 160, the first lens assembly 162, thesecond reflecting mirror assembly 164, the modulating means 166 and thesecond lens assembly 168 exist within the first space 326. The secondspace 328 includes the third lens assembly 172, the third reflectingmirror assembly 174, the fourth reflecting mirror assembly 176 and thefifth reflecting mirror assembly 178. The light beam passing opening 276is also present in the second space 328.

In the illustrated embodiment, an air sucking means 334 which may beconstructed of a suitable suction fan and an air discharge means 336(FIG. 6) which can be constructed of a suitable air discharge fan aredisposed in the first space 326. In relation to the air sucking means334, an air suction opening 340 having an air filter 338 disposedtherein is provided in the side wall 150. On the other hand, in relationto the air discharge means 336, an air discharge opening (not shown) isdisposed in the bottom wall 146. The air sucking means 334 sucks airinto the second housing 12 from outside through the air filter 338. Theair discharge means 336 discharges air from the second housing 12through the air discharge opening. The air discharged through the airdischarge opening advances into the first housing 10 from an opening(not shown) formed in the upper wall 18 (FIG. 3) of the first housing 10corresponding to the air discharge opening, and thereafter, dischargedoutside through an opening (not shown) formed at a suitable site of thefirst housing 10. By the cooperation of the air sucking means 334 withthe air discharge means 336, an air current flowing near the light beamgenerating means 158 is set up in the first space 326 as shown by anarrow 342 in FIGS. 4 and 6, and the light beam generating means 158 iscooled by this air current.

In one embodiment of this invention, the amount of air sucked by the airsuction means 334 is made larger than the amount of air discharged bythe air discharge means 336. It will be easily seen that as a result, atleast the vicinity of the air sucking opening 340 within the first space326 is maintained exactly under positive pressures. On the other hand,as is clearly seen by reference to FIGS. 4 and 6, the vent openings 330formed in the first partitioning wall 322 for air communication betweenthe first and second spaces 326 and 328 are sufficiently away from theair discharge opening (not shown) and in proximity to the air suckingopening 340. Accordingly, as shown by the arrow 344 in FIGS. 4 and 5,air flows into the second space 328 from the first space 326 through thevent openings 330, and the second space 328 is accurately maintainedunder positive pressures. Thus, air is surely discharged from the secondspace 328 into the first housing 10 through the light beam passingopening 276 in the second space 328 and the opening 90 formed in theupper wall 18 of the first housing 10. The flowing of air from the firsthousing 10 back to the second space 328 through the opening 90 and thelight beam passing opening 276 can be surely prevented (see FIG. 13also). It is possible therefore to prevent surely the incoming of tonerand dust and dirt from the first housing 10 to the second space 328 andthe resultant adhesion of such toner and dust and dirt to the variousoptical elements (the f-θ lens 248, the mirrors 258, 274 and 268)present in the second space.

To prevent incoming of the toner and dust and dirt into the second space328 (and the first space 326) from the first housing 10 through theopening 90 (FIG. 13) and the light beam passing opening 276, the lightbeam passing opening 276 may be closed by a substantially transparentmaterial 346 such as a transparent glass or a transparent film as shownin FIG. 15 instead of positively passing air from the second space 328through the light beam passing opening 276. At this time, at least thatsurface of the member 346 which is exposed to view has non-chargeablecharacteristics in order to prevent that surface of the member 346 frombeing charged under the influence of the charging corona dischargedevice 76 (see FIG. 3) of the image-forming means 4 and from gatheringthe toner and dust and dirt. To impart non-chargeable characteristics tothe aforesaid surface of the material 346, it is possible to coat theaforesaid surface with an antistatic agent which may be a substantiallytransparent electroconductive paint. Alternatively, the member 346itself may be formed of an electrically conductive glass such as NESAglass or an electrically conductive film.

Control Means

The control means 8 will now be described.

(A) Outline of the Construction of the Control Means

With reference to FIG. 16, the control means 8 includes a centralprocessing means 348, a memory means 350 and a sequence control means352 and a panel 288 (see FIG. 1 also) disposed in the cover 20. Variousoperating switch means and display means are provided in the panel 288.Signals are fed from the various operating switch means provided in thepanel 288 into the central processing means 348 which can be constructedof a microprocessor, and a signal is also fed into the centralprocessing means 348 from a suitable device 354 such as a host computerto be combined with thb image-forming apparatus 2. The memory means 350is composed of a suitable memory such as a random access memory (RAM)and memorizes given image signals such as characters or numericalfigures. The memory means 350 feeds image signals to the sequencecontrol means 352 according to the signal fed from the centralprocessing means 348. The sequence control means 352 feeds the imagesignals from the memory means 350 to the modulating means 166 of theoptical means, and controls the various constituent elements of theimage-forming means 4 as required correspondingly to the feeding of theimage signal to the modulating means 166. When an image signal is fedfrom the sequence control means to the modulating means 166 of theoptical means 6, the modulating means 166 modulates light beams, andtherefore, a scanned light beam is projected onto theelectrostatographic material 72 (FIG. 3) of the image-forming means 4.On the other hand, when no image signal is fed to the modulating means166 from the sequence control means 352, the modulating means 166 doesnot modulate light beams, and no scanned light beam is projected ontothe electrostatographic material 72 (FIG. 3). Thus, a required latentelectrostatic image is formed as a so-called dot pattern on theelectrostatographic material 72 (FIG. 3).

FIG. 17 exemplifies letter C formed in a dot pattern. This letter C isexpressed by 12×12=144 dots. In the white dots in FIG. 17, the scannedlight beam has been projected onto the electrostatographic material 72,and in the black dots, no scanned light beam has been projected onto theelectrostatographic material 72.

Since the above construction and operation of the control means 8 areknown to those skilled in the art, a detailed description of these isomitted in the present specification.

(B) Increasing of the Image Forming Speed

Frequently, it is desired in the image-forming device 2 to increase thespeed of image formation even if this results in some reduction in thequality of the resulting image. To meet this desire, the speed of imageformation is increased as shown below in one specific embodiment of thepresent invention.

When it is desired to increase the speed of image formation, thediameter of the scanned light beam to be projected from the opticalmeans 6 is increased to n times. The increasing of the diameter of thescanned light beam can be achieved by, for example, constructing theexpander lenses 216 (FIG. 7) of the optical means 6 from zoom lenseswell known in the field of cameras, and properly operating the zoomlenses. The zoom lenses can be operated automatically by attaching asuitable operating means and feeding an operating signal to theoperating means from the central processing means 348. In addition toincreasing the diameter of the scanned light beam to n times the speedof feeding the image signals to the modulating means 166 of the opticalmeans 6 from the memory means 350 through the sequence control means 352is decreased to 1/n times, and the moving speed of theelectrostatographic material 72 in the image-forming means 4, andtherefore the rotating speed of the rotating drum 70 (FIG. 3), areincreased to n times (in which case the conveying speed of the copyingpaper is naturally increased to n times). It is easily appreciated thatas a result, the number of image signals fed per predetermined area ofthe electrostatographic material 72 (FIG. 3) is decreased to 1/2n times.By this procedure, the image forming speed can be increased to n times.

FIG. 18 exemplifies letter C formed in a dot pattern when the imageforming speed has been doubled, namely when the diameter of the scannedlight beam projected from the optical means 6 is doubled, the speed offeeding image signals to the modulating means through the sequencecontrol means 352 from the memory means 350 is decreased to 1/2, and themoving speed of the electrostatographic material 72 in the image-formingmeans 4 is doubled.

It will be easily seen by comparing FIGS. 17 and 18 that when theimage-forming speed is doubled, the letter C as shown in FIG. 18 isexpressed by 6×6=36 dots which is 1/4 of the number of dots in FIG. 17(12×12=144). Since the display are of the letter C is the same for both,the letter C in FIG. 18 has an inferior image quality to that in FIG. 17because of the decrease of the number of dots.

While the present invention has been described in detail hereinabovewith regard to specific embodiments of the image-forming apparatusconstructed in accordance with this invention with referece to theaccompanying drawings, it is to be understood that the invention is notlimited to these specific embodiments, and various changes andmodifications are possible without departing from the scope of theinvention.

What is claimed is:
 1. An optical adjusting method in an image-formingapparatus comprising an optical means for projecting a scanned lightbeam to be controlled according to an image to be formed, anelectrostatic image-forming means for receiving the scanned light beamprojected from the optical means and forming an image corresponding tothe scanned light beam, and a control means for controlling the opticalmeans and the image-forming means, said optical means including a lightbeam generating means, a modulating means to which image signalscorresponding to the image to be formed are fed from the control meansand which modulates a light beam received from the light beam generatingmeans according to the image signals, and a scanning means for scanningthe light beam received from the modulating means; which comprisespositioning an adjusting jig having at least two beam holes formed atpredetermined positions between the modulating means and the scanningmeans, and adjusting the position of the modulating means such that themodulated primary beam from the modulating means passes through one ofthe beam holes and the non-modulated beam from the modulating meanspasses through the other beam hole.
 2. The method of claim 1 wherein theoptical means further includes a condensing lens disposed between thelight beam generating means and the modulating means, and the methodfurther comprises prior to the adjustment of the position of themodulating means, positioning an adjusting jig having formed at apredetermined position at least one beam hole between the condensinglens and the modulating means, and adjusting the position of thecondensing lens such that a light beam which has passed through thecondensing lens passes through the beam hole.
 3. The method of claim 2whereinthe optical means includes a reflecting mirror disposed betweenthe condensing lens and the modulating means, the predetermined positionat which the adjusting jig is positioned at the time of adjusting theposition of the condensing lens is between the condensing lens and thereflecting mirror, and said method further comprises after theadjustment of the position of the condensing lens but before theadjustment of the modulating means, positioning an adjusting jig havingformed at least one beam hole at a predetermined position thereof at apredetermined position between the modulating means and the scanningmeans, detaching the modulating means, and adjusting the position of thereflecting mirror such that the reflected light beam from the reflectingmirror passes through the beam hole.
 4. The method of claim 3 wherein inperforming the adjustment of the position of the reflecting mirror, thesame adjusting jig as in the adjustment of the position of themodulating means is positioned at the same position, and the position ofthe reflecting mirror is adjusted such that the reflected beam from thereflecting mirror passes through the other of the beam holes.
 5. Themethod of claim 2 whereinthe optical means includes a reflecting mirrordisposed between the light beam generating means and the condensinglens, and said method further comprises, prior to the adjustment of theposition of the condensing lens, positioning an adjusting jig havingformed at a predetermined position thereof at least one beam hole and anadjusting jig having formed at a predetermined position thereof at leastone beam hole between the condensing lens and the modulating means,detaching the condensing lens, an adjusting the position of thereflecting mirror such that the reflected light beam from the reflectingmirror passes through the two beam holes.
 6. The method of claim 5wherein in adjusting the position of the reflecting mirror, the sameadjusting jig as in the case of adjusting the position of the condensinglens is positioned at the same position between the condensing lens andthe modulating means.
 7. The method of claim 5 which further comprises,prior to the adjusting of the position of the reflecting mirror,positioning an adjusting jig having formed at a predetermined positionthereof at least one beam hole at a predetermined position between thelight beam generating means and the reflecting mirror, and adjusting theposition of the light beam generating means such that the light beamfrom the light beam generating means passes through the beam hole. 8.The method of claim 7 wherein the beam hole formed in the adjusting jigused in adjusting the position of the light beam generating means is ahorizontally extending elongated hole.